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A hora civil de Greenwich= 10:00 se encuentran en situación estimada= 31º 33,2´N – 121º 38,2´W y toman altura instrumental a la estrella Vega= 76º 50´22´´ con corrección de índice del sextante= +4´ y elevación del observador de 3 metros y con la hoja del Almanaque Náutico del año en vigor correspondiente a las correcciones para obtener la altura verdadera de Sol y Estrellas, calculan la altura verdadera de Vega:At HcG = 10:00 in DR position 31º 33.2' N, 121º 38.2' W, the sextant altitude of the star Vega is 76º 50' 22'' with index correction = +4' and height of eye 3 m. Calculate Vega's true altitude:
Show the answer
Correct answer: a) 76º 50' 58''
Why it is correct
Adding Ci = +4′ to 76º 50′ 22″ gives ao = 76º 54′ 22″. Subtracting dip for 3 m (−3.1′ = −3′ 06″) and refraction at 77º (−0.3′ = −18″), or −3′ 24″ in total, leaves av = 76º 50′ 58″.
Why the others are not
- b) Subtracts the index correction (+4′) instead of adding it.
- c) Subtracts over 20′ without justification for a star.
- d) Subtracts half a degree from the sextant altitude.
How to work it out in the exam
- +4.0′ (Ci) − 3.1′ (dip at 3 m) − 0.3′ (refraction at 77º) = +0.6′ (+36″).
Where this question comes from
- Región de Murcia · 2024 · 2ª convocatoria · CY Tipo 1 · question 18 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.